JP3273535B2 - Double tuning circuit of TV tuner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-tuned circuit of a TV (television) tuner, and more particularly, to a variation of a frequency-amplitude characteristic (frequency response) with respect to an intermediate frequency signal output from a frequency conversion unit of the TV tuner. And a double tuning circuit of the TV tuner in which the frequency response of a signal output from the TV tuner is improved.

[0002]

2. Description of the Related Art Generally, a TV tuner includes a high-frequency amplifier for amplifying a received signal received by a receiving antenna, a frequency converter for mixing a received signal and a local oscillation signal to obtain a mixed signal, and a local oscillation signal. , A local oscillator for selecting an intermediate frequency signal from the mixed signals (corresponding to an intermediate frequency transformer, and usually constituted by a double tuning circuit), and an intermediate frequency for amplifying the intermediate frequency signal A frequency amplification stage.

FIG. 10 is a circuit diagram showing an example of the configuration of such a known intermediate frequency selector, that is, a double tuning circuit. FIG. 11 is a circuit diagram showing an intermediate frequency output from the known double tuning circuit. FIG. 4 is a characteristic diagram illustrating an example of an ideal frequency response to a signal.

[0004] As shown in FIG.
It comprises a primary side tuning circuit 51 and a secondary side tuning circuit 52,
The input terminal of the primary-side tuning circuit 51 is coupled to the output terminal of the preceding-stage frequency converter, and the output terminal of the secondary-side tuning circuit 52 is coupled to the input terminal of the next-stage intermediate frequency amplifier. The primary-side tuning circuit 51 includes a first adjustable inductor 53, a first capacitor 54, and a first damping resistor 55 connected in parallel with each other, and the secondary-side tuning circuit 52 is connected in parallel with each other. A second adjustable inductor 56, a second capacitor 57, and a second damping resistor 58. The first and second adjustable inductors 53 and 56 are inductively coupled to form a double-tuned circuit. Is configured.

In FIG. 11, the vertical axis indicates the output signal amplitude and the horizontal axis indicates the frequency. A point P in the pass band indicates a point coincident with the resonance frequency of the primary side tuning circuit 51, and an S point Indicates a point where the resonance frequency matches the resonance frequency of the secondary-side tuning circuit 52.

In such a known double-tuned circuit, each inductance value of the first adjustable inductor 53 and the second adjustable inductor 56, and the first
By adjusting the inductive coupling states of the second adjustable inductors 53 and 56, respectively, the intermediate frequency signal obtained at the output side of the double-tuned circuit has an ideal frequency response as shown in FIG. I have to.

[0007]

In a TV tuner, the frequency response of an intermediate frequency signal output from a frequency converter usually differs depending on the receiving channel of the TV tuner.
When the gain of the high-frequency amplifier changes due to automatic gain control (AGC), the frequency response changes accordingly.

When a known double-tuned circuit is used in the intermediate frequency selection section of the TV tuner, the double-tuned circuit is adjusted as described above when one reception channel is received.
The intermediate frequency signal obtained at the output side of the double tuning circuit is shown in FIG.
Even if it shows an ideal frequency response as shown in the figure, the signal level of the received signal changes,
When the automatic gain control voltage applied to the high-frequency amplifier changes accordingly, the amplification degree of the high-frequency amplifier changes, or when the reception is switched to another reception channel, the intermediate frequency output from the frequency converter is output. Since the frequency response of the signal changes, the intermediate frequency signal obtained at the output side of the double tuning circuit does not always show the ideal frequency response as shown in FIG. If the frequency response of the intermediate frequency signal obtained at the output side of the double tuning circuit greatly changes from the ideal one, it cannot be corrected by the intermediate frequency amplifier anymore, and as a result, the output from the TV tuner The frequency response of the signal will be maladaptive.

As described above, the known double-tuned circuit has a problem that it cannot cope with a change in the frequency response of the intermediate frequency signal output from the frequency conversion unit. This is a particularly serious problem.

SUMMARY OF THE INVENTION The present invention solves such a problem, and an object of the invention is to provide a TV tuner that selectively changes a frequency response in response to a change in the frequency response of an intermediate frequency signal output from a frequency converter. It is to provide a double tuning circuit.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a combined primary and secondary tuning circuit, and the primary or secondary tuning circuit. Fukudo connected in parallel with two series circuits comprising at least one impedance element and the switching diode
An intermediate frequency selection unit that constitutes a control circuit,
The switching diode is used for each receiving channel and each receiving channel.
Of the automatic gain control voltage in the
The switching voltage is set in the control table in advance, and the TV
When a TV signal is received by the receiver, the state of the received signal
The switching voltage corresponding to
Read out and read the switching voltage corresponding to each of the above
Means are provided for selectively turning on and off each of the switching diodes by supplying the switching diodes to the switching diodes.

In the above means, in the control table , a switching voltage to be supplied to each switching diode of the double tuning circuit is set in advance for each reception channel and for each magnitude of the automatic gain control voltage in each reception channel,
When a TV signal is received by a TV tuner , a preset value corresponding to the receiving channel and the magnitude of the automatic gain control voltage is set.
The switching voltage is supplied to each switching diode, and an impedance element such as a damping resistor or an additional capacitance element for resonance is selectively connected in parallel with the primary side tuning circuit and / or the secondary side tuning circuit. Therefore, even if the frequency response of the intermediate frequency signal output from the frequency conversion unit changes for each reception channel and for each level of the automatic gain control voltage in each reception channel, the frequency response of the double-tuned circuit does not change. The intermediate frequency signal acting at the output of the double-tuned circuit acts like a cancellation and always has a frequency response close to the ideal form.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of a double tuning circuit of a TV tuner according to the present invention.

As shown in FIG. 1, the double-tuned circuit has one
An input terminal of the primary-side tuning circuit 1 is coupled to an output terminal of the frequency conversion unit 3 in the previous stage, and an output terminal of the secondary-side tuning circuit 2 is connected to the next-side tuning circuit 2. It is coupled to the input of the intermediate frequency amplifier 4 of the stage. The primary side tuning circuit 1
A first adjustable inductor 5, a first resonance capacitor 6, a first damping resistor 7, a second damping resistor 8, a first switching diode 9, a second switching diode 10, A first bypass capacitor 11 and a second bypass capacitor 12;
The secondary tuning circuit 2 includes a second adjustable inductor 13, a second resonance capacitor 14, and a third damping resistor 1.
5, the fourth damping resistor 16, the third switching diode 17, and the fourth switching diode 1
8, a third bypass capacitor 19, and a second bypass capacitor 20. Also, the control circuit unit 21
Is an integrated circuit (I) forming a phase locked loop (PLL).
C) 22, a first buffer resistor 23, a second buffer resistor 24, a third buffer resistor 25, and a fourth buffer resistor 26.

In this case, a first series circuit including a first adjustable inductor 5, a first resonance capacitor 6, a first damping resistor 7, a first switching diode 9, and a first bypass capacitor 11. , A second series circuit including the second damping resistor 8, the second switching diode 10, and the second bypass capacitor 12 is connected in parallel with each other, and the primary-side tuning circuit 1 is configured. A third series circuit including a second adjustable inductor 13, a second resonance capacitor 14, a third damping resistor 15, a third switching diode 17, and a third bypass capacitor 19; A fourth series circuit including the damping resistor 16, the fourth switching diode 18, and the fourth bypass capacitor 20 is connected in parallel to each other, and the secondary side tuning circuit 2 is configured. And the first
The adjustable inductor 5 and the second adjustable inductor 13 are inductively coupled to form a double-tuned circuit.

Further, the integrated circuit 22 has at least 8
Two output ports BS1 to BS8 and two control ports S
1 to S2, and internally holds a control table (not shown). The output port BS4 is connected to the UHF band selection terminal UB, the output port BS2 is connected to the VHF high band selection terminal HB, and the output port BS1 is connected to the VHF low band selection terminal LB. Output port BS
5 is a connection point between the first switching diode 9 and the first bypass capacitor 11 via the first buffer resistor 23, and the output port BS 6 is connected to the second switching diode 10 via the second buffer resistor 24. The output port BS7 is connected to the third connection point of the bypass capacitor 12
The connection point between the third switching diode 17 and the third bypass capacitor 19 via the buffer resistor 25 of
The output port BS8 is connected to a connection point between the fourth switching diode 18 and the fourth bypass capacitor 20 via the fourth buffer resistor 26. The control port S1 is connected to the SCL signal supply terminal SCL, and the control port S2 is connected to the SDA signal supply terminal SDA.

Next, FIGS. 2A to 2D are characteristic diagrams showing frequency responses of respective parts in the double-tuning circuit of the TV tuner shown in FIG. 1, and FIG. FIG. 9 is an explanatory diagram showing contents written to a control table.

In FIG. 2, (a) shows that the frequency response of the intermediate frequency signal output from the frequency mixing section is almost ideal, and (b) shows that the frequency response of the intermediate frequency signal is in the middle of the pass band. When it is protruding,
(C) shows a state in which the frequency response of the intermediate frequency signal protrudes on the high frequency side of the pass band, and (d) shows a state in which the frequency response of the intermediate frequency signal protrudes on the low frequency side of the pass band. In each of (a) to (d), the characteristic (a) represents the frequency response of the intermediate frequency signal obtained at the output of the frequency mixing unit 3, and the characteristic (b).
Is the frequency response of the double tuning circuit, and the characteristic (c) is the frequency response of the intermediate frequency signal output from the double tuning circuit.

By the way, the TV tuner adjusts the double-tuned circuit and writes the control table in the integrated circuit (IC) 22 before shipping the TV tuner.
The means for adjustment and writing will be described.

First, in the double-tuned circuit, the first and second switching diodes 9, 10 and the third and fourth switching diodes 17, 18 are cut off and the first adjustable inductor is turned on. 5th and 2nd
The first and second adjustable inductors 5 and 13 adjust the respective inductance values of the adjustable inductor 13 of FIG.
And the primary-side tuning circuit 1 is connected to the lower frequency side of the intermediate frequency pass band, for example, the characteristic (b) of FIG.
Is resonated in the vicinity of f ₁ point, also, the high-frequency side frequency of the secondary side tuned circuit 2 intermediate frequency pass band, e.g., FIGS. 2 (a)
Properties to resonate at f ₂ points near the (b), as the characteristic (b) in FIG. 2 (a), the frequency response of the intermediate frequency signal is symmetrical with respect to the center frequency f ₀ in the double-tuned circuit Set to an almost ideal state.

In the control table in the integrated circuit 22, when the TV tuner is operated to receive a signal of each channel of the VHF low band, a signal of each channel of the VHF high band, When each of the signals of each channel of is received,
The signal of each of these channels is
When each of the signals is received in the state of the weak electric field strength, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 corresponds to one of the characteristics (A) in FIGS. Therefore, as shown in FIG.
The writing of the ON or OFF information is performed in accordance with steps (1) to (6).

To explain this point in more detail, when the TV tuner receives a signal of one channel of the VHF high band at a high electric field strength, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is For example, FIG.
Assuming that the characteristic (a) of (a) is as follows, the control table is considered to correspond to the category 1 shown in FIG.
Four pieces of off information for turning off the outputs of the four output ports BS5 to BS8 are written in correspondence with the channel and the high electric field strength. When a signal of the same channel is received at a medium electric field strength, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is, for example, as shown in FIG.
If the characteristic (b) of (b) is obtained, the control table is considered to correspond to the category 2 shown in FIG.
Four pieces of ON information for turning on the outputs of the four output ports BS5 to BS8 are written in correspondence with the channel and the medium electric field strength. Further, when a signal of the same channel is received at a weak electric field strength, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is, for example, as shown in FIG.
If the solid line of the characteristic (b) of (c) becomes as shown in FIG. 3, the control table indicates that the outputs of the three output ports BS5, BS6, and BS8 correspond to the category 3 shown in FIG. Information and one output port B
One piece of off information for turning off the output of S7 is written in correspondence with the channel and the weak electric field strength.

Subsequently, when the TV tuner receives a signal of another channel of the VHF high band at a high electric field strength, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is, for example, as shown in FIG. Characteristics of 2 (c) (a)
As shown in FIG. 3, the control table includes two pieces of OFF information and two outputs for setting the outputs of the two output ports BS5 and BS6 to OFF voltage. Two pieces of ON information for turning on the outputs of the ports BS7 and BS8 are written in correspondence with the channel and the high electric field strength. When a signal of the same channel is received at a medium electric field strength, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is, for example,
If the characteristic line (a) of FIG. 2D is as shown by the solid line, it is assumed that the output of one output port BS5 is turned on in the control table, which corresponds to the category 5 shown in FIG. One ON information and three output ports BS6 to BSB
Three pieces of off information for setting the output of S8 to an off voltage are written in correspondence with the channel and the medium electric field strength. further,
When a signal of the same channel is received at a weak electric field strength, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is, for example, as shown by the dotted line of the characteristic (a) in FIG. For example, assuming that the category corresponds to the category 6 shown in FIG.
5. Two pieces of ON information for setting the output of BS6 to ON voltage and 2
Two pieces of off information for turning off the outputs of the two output ports BS7 and BS8 are written in correspondence with this channel and the weak electric field strength.

Hereinafter, similarly, all channels of the VHF high band, all channels of the VHF low band, UHF
For all the channels, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 corresponding to the electric field strength is one of the characteristics (a) of FIGS. 2 (a) to 2 (d). According to this, categories 1 to 6 shown in FIG.
Is determined, and the control table includes
The channel and the electric field strength are respectively written in the areas corresponding to the classification, and the writing of the control table is completed.

Next, the operation of the double tuning circuit shown in FIG. 1 will be described with reference to FIGS. 2 (a) to 2 (d) and FIG.

When a signal of one channel of the VHF high band is received in a strong electric field strength state in the TV tuner and an intermediate frequency signal is obtained at the output of the frequency conversion unit 3, the integrated circuit 22 For example, the frequency response of the intermediate frequency signal is shown in the characteristic (a) of FIG.
It is determined that it corresponds to the category 1 written in the control table, and the off voltage (zero or negative voltage) is generated from each of the four output ports BS5 to BS8. These off voltages are applied to the first to fourth switching diodes 9, 10, 1 and 1 via the first to fourth buffer resistors 23 to 26.
7 and 18, and switching diodes 9, 10,
17 and 18 are all turned off, the primary side tuning circuit 1 includes the first adjustable inductor 5 and the first resonance capacitor 6
And the secondary-side tuning circuit 2 is only a resonance circuit including the second adjustable inductor 13 and the second resonance capacitor 14. For this reason, the frequency response of the double tuning circuit is as shown in the characteristic (b) of FIG. 2A, and the frequency response of the intermediate frequency signal obtained at the output side of the double tuning circuit is shown in FIG. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

Next, assuming that the electric field strength of the signal of this channel fluctuates and the signal is received in the medium electric field intensity state, the integrated circuit 22 determines, for example, The frequency response of the frequency signal is shown in the characteristic (a) of FIG. 2B, and it is determined that the frequency response corresponds to the category 2 written in the control table, and the ON voltages (4) are output from the four output ports BS5 to BS8 respectively. Positive voltage). These ON voltages are the first
To the fourth switching diode 9, 10, 17, 1
8 are turned on, the primary-side tuning circuit 1 includes a first and second damping resistors 7 in parallel with a resonance circuit including a first adjustable inductor 5 and a first resonance capacitor 6.
8, the secondary-side tuning circuit 2 has a third and a fourth damping resistor 15 in parallel with a resonance circuit including a second adjustable inductor 13 and a second resonance capacitor 14,
16 is inserted and connected. For this reason, the frequency response of the double-tuned circuit is as shown in the characteristic (b) of FIG. 2B, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

Subsequently, assuming that the electric field strength of the signal of this channel further fluctuates and the signal is received in the weak electric field strength state, the integrated circuit 22 determines, for example, from the combination of this channel and the weak electric field strength. , The frequency response of the intermediate frequency signal is indicated by the solid line of the characteristic (a) in FIG. 2C, and it is determined that the frequency response corresponds to the category 3 written in the control table, and the three output ports BS5, BS6, BS
8 to generate an off-voltage and output port B
An on-voltage is generated from S7. These off voltages are the first, second and fourth switching diodes 9, 10, 1
8 are turned off, and the third switching diode 17 is turned off.
Is turned on, the primary-side tuning circuit 1 includes only the first adjustable inductor 5 and the first resonance capacitor 6, and the secondary-side tuning circuit 2 includes the second adjustable inductor 13 and the second adjustable inductor 13. A third damping resistor 15 is inserted and connected in parallel with a resonance circuit including the resonance capacitor 14 of FIG. For this reason, the frequency response of the double-tuned circuit is shown by the solid line of the characteristic (b) in FIG. 2C, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c) of b), the characteristic becomes substantially flat in the pass band.

Further, when the TV tuner is switched to receiving a signal of another channel of the VHF high band, and when this signal is received in a strong electric field strength state, the integrated circuit 22 is turned off.
From the combination of this channel and the strong electric field strength, for example, the frequency response of the intermediate frequency signal is shown in FIG.
The characteristic (a) is indicated by the dotted line, and it is determined that the category 4 is written in the control table, and off-voltages are generated from the two output ports BS5 and BS6, respectively.
An on-voltage is generated from each of the two output ports BS7 and BS8. These off voltages turn off the first and second switching diodes 9 and 10, and these on voltages turn on the third and fourth switching diodes 17 and 18, so that the primary side tuning circuit 1 The secondary-side tuning circuit 2 includes the second adjustable inductor 1 only in the resonance circuit including the first adjustable inductor 5 and the first resonance capacitor 6.
Third and fourth damping resistors 15 and 16 are inserted and connected in parallel to a resonance circuit including the third and second resonance capacitors 14. For this reason, the frequency response of the double-tuned circuit is shown by the dotted line of the characteristic (b) in FIG. 2C, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c) of (c), the characteristic becomes substantially flat in the pass band.

In this case, assuming that the electric field strength of the signal of this channel fluctuates and the signal is received in a medium electric field strength state, the integrated circuit 22 calculates, for example, The frequency response of the intermediate frequency signal is shown by the solid line of the characteristic (a) in FIG. 2D, and it is determined that the frequency response corresponds to the category 5 written in the control table, and the ON voltage is output from one output port BS5. And an off voltage is generated from each of the three output ports BS6 to BS8. This on voltage turns on the first switching diode 9 and these off voltages turn off the second to fourth switching diodes 10, 17, and 18, so that the primary-side tuning circuit 1 has the first adjustable A first damping resistor 7 is inserted and connected in parallel with a resonance circuit including the inductor 5 and the first resonance capacitor 6, and the secondary-side tuning circuit 2 includes a second adjustable inductor 13 and a second resonance capacitor. 14 only. For this reason, the frequency response of the double-tuned circuit is shown by the solid line of the characteristic (b) in FIG. 2D, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is
As shown in the characteristic (c) of FIG. 2D, the characteristic becomes substantially flat in the pass band.

Thereafter, assuming that the electric field strength of the signal of this channel further fluctuates and the signal is received in a weak electric field strength state, the integrated circuit 22 determines, for example, from the combination of this channel and the weak electric field strength. , The frequency response of the intermediate frequency signal is indicated by the dotted line of the characteristic (a) in FIG. 2D, and it is determined that the frequency response corresponds to the category 6 written in the control table, and the two output ports BS5 and BS6 Each generates an ON voltage, and outputs two output ports BS7 and B
An off-voltage is generated from S8. These ON voltages turn on the first and second switching diodes 9 and 10, and turn on the third and fourth switching diodes 17, 1 and 1.
Since the first tuning circuit 8 is turned on, the primary side tuning circuit 1 has first and second damping resistors 7 and 8 inserted and connected in parallel with a resonance circuit including the first adjustable inductor 5 and the first resonance capacitor 6. In addition, the secondary-side tuning circuit 2 is only a resonance circuit including the second adjustable inductor 13 and the second resonance capacitor 14. Therefore, the frequency response of the double-tuned circuit is indicated by the dotted line of the characteristic (b) in FIG. 2D, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is as shown in FIG. As shown in the characteristic (d) of d), the characteristic becomes substantially flat in the pass band.

In this case, the control table contains, as described above, still another channel of the VHF high band, VHF
For all the channels in the low band, all the channels in the UHF band, and all the combinations corresponding to the electric field strength at the time of reception, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is as shown in FIGS. Since any of the categories 1 to 6 shown in FIG. 3 is written in accordance with any one of the characteristics (a) of (d), the integrated circuit 22 receives the received channel and the electric field of the received signal. Based on the combination with the strength, it is determined which type of the control table is applicable, and an on or off voltage is output to each of the output ports BS5 to BS8 corresponding to the determined type, and the first to fourth damping is performed. Resistance 9, 10, 17, 1
8 is selectively connected in parallel to the primary-side tuning circuit 1 and / or the secondary-side tuning circuit 2 so that the frequency response of the intermediate frequency signal output from the frequency converter 3 has any characteristic. However, the frequency response of the intermediate frequency signal output from the double-tuned circuit has a substantially flat characteristic in the pass band as shown in each characteristic (c) of FIGS. 2 (a) to 2 (d). Become.

As described above, according to the present embodiment, the TV
Depending on the characteristics of each part of the tuner, even if the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 changes in accordance with the reception channel and its electric field strength, the first to fourth circuits are added to the double tuning circuit. The damping resistances 9, 10, 17,
18 is selectively inserted and connected, and corrects the frequency response so as to approach an ideal frequency response. Therefore, the frequency response of the intermediate frequency signal output from the double tuning circuit is always substantially flat within the pass band. Can be characteristics.

FIG. 4 is a circuit diagram showing a second embodiment of the double tuning circuit of the TV tuner according to the present invention.

In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 4, the primary side tuning circuit 1
Is a first additional capacitor 27 connected in series with the first switching diode 9 in addition to a resonance circuit including the first adjustable inductor 5 and the first resonance capacitor 6.
, A second additional capacitor 28 connected in series to the first switching diode 9, and a first fixed damping resistor 29 connected in parallel to the resonance circuit. In addition to the resonance circuit including the second adjustable inductor 13 and the second resonance capacitor 14, the third
A third additional capacitor 30 connected in series to the switching diode 17, a fourth additional capacitor 31 connected in series to the fourth switching diode 18, and a second fixed damping resistor 32 connected in parallel to the resonance circuit.
And In addition to the first to fourth buffer resistors 23 to 26, the control circuit unit 21 also connects the first to fourth buffer resistors 23 to 26 between the cathodes of the first to fourth switching diodes 9, 10, 17, 18 and the ground. Fifth to eighth buffer resistors 33 to 36, which constitute the return path of the ON voltage applied to the four switching diodes 9, 10, 17, and 18, are provided.

In this case, the difference between the embodiment shown in FIG. 4 (hereinafter referred to as the former) and the embodiment shown in FIG. 1 (hereinafter referred to as the latter) is as follows.
The first to fourth elements in which the former is selectively inserted and connected to the resonance circuit
, Whereas the latter has first to fourth damping resistors 7, 8, 15, 16 selectively inserted and connected to the same resonance circuit. And the point that the former has the first and second fixed damping resistors 29 and 32, whereas the latter does not have such fixed damping resistors.
The former is the first to fourth switching diodes 9, 1
While the fifth to eighth buffer resistors 33 to 36 are provided for returning the ON voltages applied to 0, 17, and 18, the latter are provided with the fifth to eighth buffer resistors 33 to 36. There is no other structural difference between the former and the latter. Therefore, further description of the configuration in the present embodiment will be omitted.

FIGS. 5A to 5E are characteristic diagrams showing the frequency response of each part in the double-tuning circuit of the TV tuner shown in FIG. 4, and FIG. FIG. 9 is an explanatory diagram showing contents written to a control table.

In FIG. 5, (a) shows that the frequency response of the intermediate frequency signal output from the frequency mixing section is almost ideal, and (b) shows that the frequency response of the intermediate frequency signal is lower than the pass band. (C) shows a state where the frequency response of the same intermediate frequency signal protrudes on the high side or low side of the pass band, and (d) shows a state where the frequency response of the intermediate frequency signal protrudes toward the high side or the high side. When the frequency response of the signal spreads on both the low band side and the high band side of the pass band, (e) shows that the frequency response of the same intermediate frequency signal is on both the low band side and the high band side of the pass band. In each of FIGS. 3A to 3E, the characteristic (a) is the frequency response of the intermediate frequency signal obtained at the output of the frequency mixing unit 3, and the characteristic (b) is double-tuned. Circuit frequency response Characteristics (c) is the frequency response of the intermediate frequency signal output from the double-tuned circuit.

Also in this embodiment, the TV tuner adjusts the double-tuned circuit and writes it in the control table in the integrated circuit (IC) 22 before shipping.

That is, in the double-tuned circuit, the first and third switching diodes 9 and 17 are turned on and the second and third switching diodes 9 and 17 are turned on.
With the fourth switching diodes 10 and 18 turned off, the respective inductance values of the first adjustable inductor 5 and the second adjustable inductor 13 are adjusted, and the first and second adjustable inductors 5 are adjusted. , 13 are adjusted, and the primary-side tuning circuit 1 is switched to the lower frequency side of the intermediate frequency pass band, for example, f ₁ of the characteristic (b) of FIG.
Is resonated at a point near, also, the high-frequency side frequency of the secondary side tuned circuit 2 intermediate frequency passband, for example, to resonate at f ₂ points near the characteristic (b) in FIG. 2 (a), FIG. 2 (a as the characteristics (b) of), is set to nearly ideal state in which the frequency response of the intermediate frequency signal is symmetrical with respect to the center frequency f ₀ in the double-tuned circuit.

In the control table in the integrated circuit 22, when the TV tuner is operated to receive a signal of each channel of the VHF low band, a signal of each channel of the VHF high band, When each of the signals of each channel of is received,
When the signals of the respective channels are received at high electric field intensity, medium electric field intensity, and weak electric field intensity, respectively, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is shown in FIG.
Depending on which of the characteristics (a) in (a) to (e), ON or OFF information is written according to categories 1 to 7, as shown in FIG.

Here, the operation of the double tuning circuit shown in FIG. 4 will be described with reference to FIGS. 5 (a) to 5 (e) and FIG.

In the TV tuner, a signal of any one channel of the VHF high band, the VHF low band, or the UHF band is received, for example, in a strong electric field strength state. When obtained, the integrated circuit 22 determines from the combination of the channel and the strong electric field strength that, for example, the frequency response of the intermediate frequency signal is shown in the characteristic (a) of FIG. It is determined that the written data corresponds to the category 1, and the on-voltage is generated from the two output ports BS5 and BS7, and the two output ports BS6 and BS are output.
8 generates an off-voltage. The on-voltage is first,
It is applied to the first and third switching diodes 9 and 17 via the third buffer resistors 23 and 25 to turn them on, and the off voltage is changed to the second and fourth buffer resistors 24 and 24.
26, the second and fourth switching diodes 1
0, 18 and these are turned off, so that the primary-side tuning circuit 1 becomes a resonance circuit including the first adjustable inductor 5, the first resonance capacitor 6, and the first additional capacitor 27. The secondary side tuning circuit 2 is a resonance circuit including the second adjustable inductor 13, the second resonance capacitor 14, and the first additional capacitor 30. For this reason,
The frequency response of the double tuning circuit is shown in the characteristic (b) of FIG. 5A, and the frequency response of the intermediate frequency signal obtained at the output side of the double tuning circuit is shown in FIG.
As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

Next, when the selection of the channel is switched and the signal of the second channel is received, for example, in the medium electric field strength state, the integrated circuit 22 determines, for example, from the combination of the second channel and the medium electric field strength, The frequency response of the intermediate frequency signal is shown by the solid line of the characteristic (a) in FIG. 5B, and it is determined that the frequency response corresponds to the category 2 written in the control table, and the ON voltage is output from one output port BS5. And an off voltage is generated from each of the three output ports BS6 to BS8. The ON voltage turns on the first switching diode 9 and the OFF voltage turns on the second to fourth switching diodes.
Are turned off, the primary-side tuning circuit 1 is switched to a resonance circuit including the first adjustable inductor 5, the first resonance capacitor 6, and the first additional capacitor 27. Thus, the secondary-side tuning circuit 2 is a resonance circuit including the second adjustable inductor 13 and the second resonance capacitor 14. For this reason, the frequency response of the double tuning circuit is shown by the solid line of the characteristic (b) in FIG. 5B, and the frequency response of the intermediate frequency signal obtained at the output side of the double tuning circuit is shown in FIG. As shown in the characteristic (c) of b), the characteristic becomes substantially flat in the pass band.

Subsequently, when the channel selection is switched and the signal of the third channel is received, for example, in the weak electric field strength state, the integrated circuit 22 determines, for example, the combination of the third channel and the weak electric field strength. The frequency response of the intermediate frequency signal is indicated by the dotted line of the characteristic (a) in FIG. 5B, and it is determined that the frequency response corresponds to the category 3 written in the control table, and the three output ports BS5 and BS6 , BS
8 to generate an off-voltage and output port B
An on-voltage is generated from S7. These off voltages are the first, second and fourth switching diodes 9, 10, 1
8 is turned off, and the third switching diode 17 is turned off.
Is turned on, the primary-side tuning circuit 1 becomes a resonance circuit including the first adjustable inductor 5 and the first resonance capacitor 6, and the secondary-side tuning circuit 2 becomes the second adjustable inductor. 13, a second resonance capacitor 14, and a third additional capacitor 30. For this reason,
The frequency response of the double-tuned circuit is shown by the dotted line of the characteristic (b) in FIG. 5B, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG.
As shown in the characteristic (c) of (b), the characteristic becomes substantially flat in the pass band.

Further, when the signal of the fourth channel is received by switching the channel selection, for example, in a strong electric field strength state, the integrated circuit 22 determines, for example, from the combination of the fourth channel and the strong electric field strength. The frequency response of the intermediate frequency signal is indicated by the solid line of the characteristic (a) in FIG. 5C, and it is determined that the frequency response corresponds to the category 4 written in the control table, and the four output ports BS5 to BS8 respectively output the response. Generates ON voltage. Since these ON voltages turn on all of the first to fourth switching diodes 9, 10, 17, and 18, the primary-side tuning circuit 1 includes the first adjustable inductor 5 and the first resonance capacitor 6 , A first additional capacitor 27, and a second additional capacitor 28, and the secondary-side tuning circuit 2 includes a second adjustable inductor 13, a second resonance capacitor 14, and a third
Is a resonance circuit including the additional capacitor 30 of FIG. For this reason, the frequency response of the double tuning circuit is shown by the solid line of the characteristic (b) in FIG. 5C, and the frequency response of the intermediate frequency signal obtained at the output side of the double tuning circuit is shown in FIG. As shown in the characteristic (c) of (c), the characteristic becomes substantially flat in the pass band.

Next, when the selection of the channel is switched and the signal of the fifth channel is received, for example, in the medium electric field strength state, the integrated circuit 22 determines, for example, from the combination of the fifth channel and the medium electric field strength, The frequency response of the intermediate frequency signal is shown by the dotted line of the characteristic (a) in FIG. 5C, and it is determined that the frequency response corresponds to the category 5 written in the control table, and the four output ports BS5 to BS8 output Each generates an off-voltage. These off voltages are the first
To the fourth switching diode 9, 10, 17, 1
8 are all turned off, the primary side tuning circuit 1
And the secondary-side tuning circuit 2 becomes a resonance circuit consisting of the second adjustable inductor 13 and the second resonance capacitor 14. . For this reason, the frequency response of the double-tuned circuit is shown by the dotted line of the characteristic (b) in FIG. 5C, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c) of (c), the characteristic becomes substantially flat in the pass band.

Subsequently, when the channel selection is switched and a signal of the sixth channel is received, for example, in a weak electric field strength state, the integrated circuit 22 determines, for example, from the combination of the sixth channel and the weak electric field strength. , The frequency response of the intermediate frequency signal is shown in the characteristic (a) of FIG. 5D, and it is determined that the frequency response corresponds to the category 6 written in the control table, and the two output ports BS5 and BS6 respectively output An off voltage is generated, and an on voltage is generated from each of the two output ports BS7 and BS8. The off voltage is the first, second
The switching diodes 9 and 10 are turned off, and the on-voltage is changed to the third and fourth switching diodes 17 and 1.
8, the primary side tuning circuit 1 is a resonance circuit including the first adjustable inductor 5 and the first resonance capacitor 6, and the secondary side tuning circuit 2 is the second adjustable inductor. 13, a second resonance capacitor 14, a third additional capacitor 30, and a fourth additional capacitor 18. For this reason, the frequency response of the double-tuned circuit is as shown in the characteristic (b) of FIG. 5D, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

Further, when the signal of the seventh channel is received by switching the channel selection, for example, in the medium electric field strength state, the integrated circuit 22 determines, for example, from the combination of the seventh channel and the medium electric field strength. The frequency response of the intermediate frequency signal is shown in the characteristic (a) of FIG. 5 (e), and it is determined that the frequency response corresponds to the category 7 written in the control table, and the two output ports BS5 and BS6 are turned on respectively. A voltage is generated, and an off voltage is generated from each of the two output ports BS7 and BS8. The ON voltage is the first, second
Of the switching diodes 9 and 10 are turned on, and the off voltage is changed to the third and fourth switching diodes 17 and 1.
8 is turned off, the primary-side tuning circuit 1 becomes a resonance circuit including the first adjustable inductor 5, the first resonance capacitor 6, the first additional capacitor 27, and the second additional capacitor 28. Thus, the secondary-side tuning circuit 2 is a resonance circuit including the second adjustable inductor 13 and the second resonance capacitor 14. For this reason, the frequency response of the double tuning circuit is as shown in the characteristic (b) of FIG. 5 (e), and the frequency response of the intermediate frequency signal obtained at the output side of the double tuning circuit is shown in FIG. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

In this case, as described above, the control table includes, for each channel of the VHF high band, each channel of the VHF low band, each channel of the UHF band, and all combinations corresponding to the electric field strength at the time of reception. According to whether the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is one of the characteristics (A) in FIGS. 5A to 5E, the frequency response is classified into any of the categories 1 to 7 shown in FIG. Since the relevant information is written, the integrated circuit 22
Based on the combination of the received channel and the electric field strength of the received signal, it is determined which type of the control table is applicable, and the on or off voltage is output to each of the output ports BS5 to BS8 in accordance with the determined type. , The first to fourth additional capacitors 27, 28, 30, 31 are selectively inserted and connected in parallel to the primary-side tuning circuit 1 and / or the secondary-side tuning circuit 2, so that the output from the frequency converter 3 is output. Regardless of the characteristic of the frequency response of the intermediate frequency signal to be output, the frequency response of the intermediate frequency signal output from the double-tuned circuit is the characteristic (c) shown in FIGS. As shown in (1), the characteristic becomes substantially flat in the pass band.

As described above, according to the present embodiment, the TV
Depending on the characteristics of each part of the tuner, even if the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 changes in accordance with the reception channel and its electric field strength, the first to fourth circuits are added to the double tuning circuit. Additional capacitors 27, 28, 3
0 and 31 are selectively inserted and connected, and the frequency response is corrected so as to approach an ideal frequency response. Therefore, the frequency response of the intermediate frequency signal output from the double-tuned circuit is always substantially within the pass band. Flat characteristics can be obtained.

FIG. 7 is a circuit diagram showing a third embodiment of the double tuning circuit of the TV tuner according to the present invention.

In FIG. 7, the same components as those shown in FIG. 4 are denoted by the same reference numerals.

As shown in FIG. 7, the primary side tuning circuit 1
Is a fifth damping resistor connected in series to the first switching diode 9 in addition to a resonance circuit including the first adjustable inductor 5, the first resonance capacitor 6, and the first fixed damping resistor 29. 37, and a fifth additional capacitor 38 connected in series to the second switching diode 10. The secondary tuning circuit 2 includes a second adjustable inductor 13, a second resonance capacitor 14, and a second resonance capacitor 14. In addition to the resonance circuit consisting of the fixed damping resistor 32 of FIG.
And a sixth damping resistor 40 connected in series to the fourth switching diode 18. Further, in addition to the first to fourth buffer resistors 23 to 26, the control circuit unit 21 connects the second and third switching diodes 10 and 17 between the cathode and the ground point.
And the ninth and tenth buffer resistors 41 and 42 forming the return path of the ON voltage applied to the third switching diodes 10 and 17.

In this case, the difference between the embodiment shown in FIG. 7 (hereinafter referred to as the former) and the embodiment shown in FIG. 4 (hereinafter referred to as the latter) is as follows.
Fifth and sixth wherein the former is selectively inserted and connected to the resonance circuit
Of the first to fourth additional capacitors 27, 28 selectively inserted and connected to the same resonance circuit, while the additional capacitors 38, 39 and the fifth and sixth damping resistors 37, 40 are provided. , 30, 31; the former is the second and third switching diodes 10, 17,
Ninth and tenth buffer resistors 41 and 42 that constitute the return path of the ON voltage applied to the
To the fourth switching diode 9, 10, 17, 1
Only the fifth to eighth buffer resistors 33 to 36 that constitute the return path of the on-voltage applied to 8 are provided, and there is no difference in configuration between the former and the latter.
Therefore, in the present embodiment, further description of the configuration is omitted.

FIGS. 8A to 8D are characteristic diagrams showing the frequency response of each part in the double-tuning circuit of the TV tuner shown in FIG. 7, and FIG. FIG. 9 is an explanatory diagram showing contents written to a control table.

In FIG. 8, (a) shows the case where the frequency response of the intermediate frequency signal output from the frequency mixing section is almost ideal, and (b) shows the frequency response of the intermediate frequency signal in the high band of the pass band. When the side is protruding,
(C) is a state where the frequency response of the same intermediate frequency signal protrudes on the lower side of the pass band, and (d) is a frequency response of the same intermediate frequency signal on both the lower side and the higher side of the pass band. (E) shows a case where the frequency response of the intermediate frequency signal is narrowing on both the low band side and the high band side of the pass band, and (a) to (e). In e), the characteristic (a) is obtained at the frequency response of the intermediate frequency signal obtained at the output of the frequency mixing unit 3, the characteristic (b) is obtained at the frequency response of the double tuning circuit, and the characteristic (c) is obtained at the output of the double tuning circuit. This is the frequency response of the intermediate frequency signal.

Also in the present embodiment, the TV tuner adjusts the double-tuned circuit and writes it in the control table in the integrated circuit (IC) 22 before shipping.

That is, in the double tuning circuit, the first and second switching diodes 10 and 17 are turned on, and the first and fourth switching diodes 9 and 18 are turned off. 5 and the second adjustable inductor 13 are adjusted, the degree of coupling between the first and second adjustable inductors 5 and 13 is adjusted, and the primary side tuning circuit 1 is adjusted to a low intermediate frequency pass band. The band side frequency, for example, f ₁ of the characteristic (b) of FIG.
Is resonated at a point near, also, the high-frequency side frequency of the secondary side tuned circuit 2 intermediate frequency passband, for example, to resonate at f ₂ points near the characteristic (b) in FIG. 2 (a), FIG. 2 (a as the characteristics (b) of), is set to nearly ideal state in which the frequency response of the intermediate frequency signal is symmetrical with respect to the center frequency f ₀ in the double-tuned circuit.

In the control table in the integrated circuit 22, when the TV tuner is operated to receive a signal of each channel of the VHF low band, a signal of each channel of the VHF high band, When each of the signals of each channel of is received,
When the signals of the respective channels are received with high electric field intensity, medium electric field intensity, and weak electric field intensity, respectively, the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 is shown in FIG.
Depending on which of the characteristics (a) among (a) to (e), ON or OFF information is written according to categories 1 to 5, as shown in FIG.

Here, the operation of the double tuning circuit shown in FIG. 7 will be described with reference to FIGS. 8 (a) to 8 (e) and FIG.

In the TV tuner, a signal of any one channel of the VHF high band, the VHF low band, or the UHF band is received, for example, in a strong electric field strength state, and an intermediate frequency signal is output to the output of the frequency conversion unit 3. When obtained, the integrated circuit 22 determines from the combination of the channel and the strong electric field strength, for example, that the frequency response of the intermediate frequency signal is as shown in the characteristic (a) of FIG. It is determined that the data corresponds to the category 1 in which the data is written, and an on-voltage is generated from each of the two output ports BS6 and BS7.
8 generates an off-voltage. The ON voltage is second,
Since the third switching diodes 10 and 17 are turned on and the off voltage turns the first and fourth switching diodes 9 and 18 off, the primary-side tuning circuit 1 is connected to the first adjustable inductor 5 and the The second tuning circuit 2 includes a second adjustable inductor 13, a second resonance capacitor 14, and a first resonance capacitor 6, a first fixed damping resistor 29, and an additional capacitor 38. 2 fixed damping resistor 32 and sixth additional capacitor 3
9 is obtained. For this reason, the frequency response of the double-tuned circuit is as shown in the characteristic (b) of FIG. 8A, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

Next, when the selection of the channel is switched and the signal of the second channel is received, for example, in the medium electric field strength state, the integrated circuit 22 determines, for example, from the combination of the second channel and the medium electric field strength. The frequency response of the intermediate frequency signal is shown in the characteristic (a) of FIG. 8B, and it is determined that the frequency response corresponds to the category 2 written in the control table, and an ON voltage is generated from one output port BS7. Then, an off-voltage is generated from each of the three output ports BS5, BS6, and BS8. The ON voltage turns on the third switching diode 17, and the OFF voltage turns off the first, second, and fourth switching diodes 9, 10, and 18. Therefore, the primary-side tuning circuit 1 The resonance circuit includes an adjustable inductor 5, a first resonance capacitor 6, and a first fixed damping resistor 29. The secondary tuning circuit 2 includes a second adjustable inductor 13 and a second resonance capacitor 14. And the second fixed damping resistor 32 and the sixth
And a resonance circuit comprising the additional capacitor 39 of FIG. Therefore, the frequency response of the double-tuned circuit is as shown in the characteristic (b) of FIG. 8B, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is as shown in FIG.
As shown in the characteristic (c) of (b), the characteristic becomes substantially flat in the pass band.

Subsequently, when the channel selection is switched and a signal of the third channel is received, for example, in a weak electric field strength state, the integrated circuit 22 determines, for example, from the combination of the third channel and the weak electric field strength. , The frequency response of the intermediate frequency signal is as shown in the characteristic (a) of FIG. 8C, and it is determined that the frequency response corresponds to the category 3 written in the control table, and the two output ports BS5 and BS6 respectively output An on-voltage is generated, and an on-voltage is generated from two output ports BS7 and BS8. These ON voltages are the first, second
Are turned on, and the third and fourth switching diodes 17 and 18 are turned off, so that the primary-side tuning circuit 1 includes the first adjustable inductor 5 and the first resonance capacitor. 6, a first fixed damping resistor 29, a fifth damping resistor 37, and a fifth additional capacitor 38, and the secondary-side tuning circuit 2 is connected to the second adjustable inductor 13 and the second resonance circuit. A resonance circuit including the capacitor 14 for use and the second fixed damping resistor 32. For this reason, the frequency response of the double-tuned circuit is as shown in the characteristic (b) of FIG. 8C, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

Further, when the signal of the fourth channel is received by switching the channel selection, for example, in the strong electric field strength state, the integrated circuit 22 determines, for example, from the combination of the fourth channel and the strong electric field strength. The frequency response of the intermediate frequency signal is shown in the characteristic (a) of FIG.
It is determined that the data corresponds to the category 4 written in the control table, and an ON voltage is generated from one output port BS5.
An off voltage is generated from each of the output ports BS6 to BS8. Since the ON voltage turns on the first switching diode 9 and the OFF voltage turns off the second to fourth switching diodes 10, 17, and 18, the primary-side tuning circuit 1 includes the first adjustable inductor. 5, a first resonance capacitor 6, and a first fixed damping resistor 2.
9 and a fifth damping resistor 37, and the secondary-side tuning circuit 2 is a resonance circuit including the second adjustable inductor 13, the second resonance capacitor 14, and the second fixed damping resistor 32. Circuit. Therefore, the frequency response of the double-tuned circuit is as shown in the characteristic (b) of FIG. 8D, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is shown in FIG. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

Next, when the selection of the channel is switched and the signal of the fifth channel is received, for example, in the medium electric field strength state, the integrated circuit 22 determines, for example, from the combination of the fifth channel and the medium electric field strength, The frequency response of the intermediate frequency signal is shown in the characteristic (a) of FIG. 8 (e), and it is determined that the frequency response corresponds to the category 5 written in the control table, and the three output ports BS5, BS7, and BS8 output An off voltage is generated, and an on voltage is generated from one output port BS6. These off voltages turn the first, third, and fourth switching diodes 9, 17, and 18 off, and turn on the second switching diode 10, so that the primary-side tuning circuit 1 has the first The resonance circuit includes the adjustment inductor 5, the first resonance capacitor 6, the first fixed damping resistor 29, and the fifth additional capacitor 38, and the secondary tuning circuit 2 includes the second adjustment inductor 13 and the second adjustment inductor 13. The resonance circuit is composed of the second resonance capacitor 14 and the second fixed damping resistor 32. For this reason, the frequency response of the double-tuned circuit is as shown in the characteristic (b) of FIG. 8E, and the frequency response of the intermediate frequency signal obtained at the output side of the double-tuned circuit is as shown in FIG.
As shown in the characteristic (c) of (e), the characteristic becomes substantially flat in the pass band.

Also in this case, the control table contains
As described above, each channel of the VHF high band, VHF
The frequency response of the intermediate frequency signal output from the frequency conversion unit 3 for each of the low band channels, the UHF band channels, and all the combinations corresponding to the electric field strength at the time of reception is shown in FIGS. Characteristics (a)
9 is written according to which of the categories 1 to 5 shown in FIG. 9, the integrated circuit 22 performs control based on the combination of the received channel and the electric field strength of the received signal. It is determined which type of the table corresponds, and the ON or OFF voltage is output to each of the output ports BS5 to BS8 in accordance with the determined type, and the fifth,
The frequency conversion is performed by selectively inserting and connecting the sixth damping resistors 37 and 40 and the fifth and sixth additional capacitors 38 and 39 in parallel to the primary tuning circuit 1 and / or the secondary tuning circuit 2. Regardless of the characteristics of the frequency response of the intermediate frequency signal output from the section 3, the frequency response of the intermediate frequency signal output from the double-tuned circuit is as shown in FIGS. As shown in the characteristic (c), the characteristic becomes substantially flat in the pass band.

As described above, according to the present embodiment, the TV
Depending on the characteristics of each part of the tuner, even if the frequency response of the intermediate frequency signal output from the frequency conversion unit 3 changes in accordance with the reception channel and its electric field strength, the fifth and sixth tunable circuits are added to the double tuning circuit. The damping resistors 37 and 40 and the fifth and sixth additional capacitors 38 and 39 are selectively inserted and connected to correct the frequency response so as to approach an ideal frequency response. The frequency response of the intermediate frequency signal can always have a substantially flat characteristic in the pass band.

In the present embodiment, the information to be written into the control table is classified into five types, 1 to 5. However, other types of information in the control table, for example, as type 6, as BS5 ON, BS6 On, BS7 on, BS8 on, as category 7, BS5 off, BS6 off, B
Of course, it is also possible to write the one with S7 off and BS8 off.

[0072]

As described above in detail, according to the present invention, a control table is supplied to each switching diode of the double tuning circuit for each receiving channel and for each level of the automatic gain control voltage in each receiving channel. have set up switching voltage in advance to, when receiving the TV signals in TV tuner, to supply the preset switching voltage corresponding to the magnitude of the reception channel and automatic gain control voltage to each of the switching diodes, 1 Secondary side tuning circuit and / or
Alternatively, an impedance element such as a damping resistor or an additional capacitance element for resonance is selectively connected in parallel with the secondary-side tuning circuit, so that each reception channel and the magnitude of the automatic gain control voltage in each reception channel are different. In addition, even if the frequency response of the intermediate frequency signal output from the frequency conversion unit changes, the frequency response of the double tuning circuit works to cancel the change, and the intermediate frequency signal obtained at the output side of the double tuning circuit is There is an effect that a frequency response close to an ideal shape can always be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a double tuning circuit of a TV tuner according to the present invention.

FIG. 2 is a characteristic diagram illustrating a frequency response of each unit in a double tuning circuit of the TV tuner illustrated in FIG. 1;

FIG. 3 is an explanatory diagram showing contents written to a control table in an integrated circuit in the double tuning circuit of the TV tuner shown in FIG. 1;

FIG. 4 is a circuit diagram showing a second embodiment of the double tuning circuit of the TV tuner according to the present invention.

5 is a characteristic diagram showing a frequency response of each unit in the double tuning circuit of the TV tuner shown in FIG.

6 is an explanatory diagram showing contents written to a control table in an integrated circuit in the double-tuned circuit of the TV tuner shown in FIG. 4;

FIG. 7 is a circuit diagram showing a third embodiment of the double tuning circuit of the TV tuner according to the present invention.

8 is a characteristic diagram showing a frequency response of each unit in the double tuning circuit of the TV tuner shown in FIG.

9 is an explanatory diagram showing contents written to a control table in an integrated circuit in the double tuning circuit of the TV tuner shown in FIG. 7;

FIG. 10 is a circuit configuration diagram showing an example of a double tuning circuit of a known TV tuner.

FIG. 11 is a characteristic diagram showing an example of an ideal frequency response of the intermediate frequency signal at the output side of the double tuning circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Primary side tuning circuit 2 Secondary side tuning circuit 3 Frequency conversion part 4 Intermediate frequency amplifying part 5 First adjustable inductor 6 First resonance capacitor 7 First damping resistor 8 Second damping resistor 9 First Switching diode 10 second switching diode 11 first bypass capacitor 12 second bypass capacitor 13 second adjustable inductor 14 second resonance capacitor 15 third damping resistor 16 fourth damping resistor 17 third Switching diode 18 fourth switching diode 19 third bypass capacitor 20 fourth bypass capacitor 21 control circuit unit 22 integrated circuit (IC) 23 first buffer resistor 24 second buffer resistor 25 third buffer resistor 26 Fourth buffer resistor 27 Denser 28 Second additional capacitor 29 First fixed damping resistor 30 Third additional capacitor 31 Fourth additional capacitor 32 Second fixed damping resistor 33 Fifth buffer resistor 34 Sixth buffer resistor 35 Seventh buffer Resistance 36 Eighth buffer resistance 37 Fifth damping resistance 38 Fifth additional capacitor 39 Sixth additional capacitor 40 Sixth damping resistance 41 Ninth buffer resistance 42 Tenth buffer resistance

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuharu Kudo 1-7, Yukitani-Otsuka-cho, Ota-ku, Tokyo Alps Electric Co., Ltd. (56) References JP-A-8-223506 (JP, A) 58-127709 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03J 5/24 H04B 1/26 H04N 5/44 H03J 3/24

Claims (5)

(57) [Claims] And 1. A primary side tuned circuit coupled and the secondary side tuned circuit, two series circuits consisting of the primary side tuned circuit or the secondary side at least one impedance element and the switching diode of the tuning circuit Duplicate connected in parallel
An intermediate frequency selection unit that constitutes a control circuit,
The switching diode is used for each receiving channel and each receiving channel.
Of the automatic gain control voltage in the
The switching voltage is set in the control table in advance, and the TV
When a TV signal is received by the receiver, the state of the received signal
The switching voltage corresponding to
Read out and read the switching voltage corresponding to each of the above
A double tuning circuit for a TV tuner, wherein each of the switching diodes is selectively turned on and off by supplying the switching diode to the switching diode. 2. The impedance element according to claim 1,
2. The double tuning circuit of a TV tuner according to claim 1, wherein the tuning circuit is a Q-damping resistance element in the primary tuning circuit and / or the secondary tuning circuit. 3. 3. The impedance element according to claim 1,
The double tuning circuit of a TV tuner according to claim 1, wherein the double tuning circuit is a part of a resonance capacitance element of the primary side tuning circuit and / or the secondary side tuning circuit. 4. The device according to claim 1, wherein the impedance element is a part of a Q-damping resistance element and a resonance capacitance element in the primary-side tuning circuit and / or the secondary-side tuning circuit. 2. The double tuning circuit of the TV tuner according to claim 1. 5. A power supply for each of said switching diodes.
The switching voltage is controlled by the control circuit unit.
Claim, characterized in that the read from the control table 1
Double-tuned circuit of a TV tuner described.